Method of system access to a wireless network

ABSTRACT

A method of system access from a wireless device to a wireless network, the network having a plurality of base stations includes the steps of: selecting at least one reverse link cost metric from a list of predetermined reverse link cost metrics; determining a reverse link cost according to the selected at least one reverse link cost metric; selecting a candidate base station from the plurality of base stations; sending a probe signal at the reverse link cost to the candidate base station; waiting for a response from the candidate base station within a timeout period; and repeating steps until timeout, or until the condition that a response is received from at least one candidate base station so that at least one candidate base station can be used to provide system access from the wireless device to the wireless network.

This application is a 371 of PCT/CA02/01944 Dec. 06, 2002 which claimsbenefit of Ser. No. 60,336,687 Dec. 07, 2001.

BACKGROUND

1. Field of the Invention

This invention relates generally to a method for system access inwireless networks. More particularly, the invention provides a methodthat may be practice at a wireless device for accessing a wirelessnetwork in a way that conserves a link cost at the wireless device. Theinvention is particularly well suited for use in Personal DigitalAssistants, mobile communication devices, cellular phones, and wirelesstwo-way communication devices (collectively referred to herein as“wireless devices”). The invention provides utility, however, in anydevice or system that accesses a wireless network.

2. Description of the Related Art

Techniques for accessing wireless networks are known. One such accesstechnique is used in current COMA (Code Division Multiple Access)networks. In a typical access technique, a wireless device probes a basestation at a given power level. If the base station does not respond,subsequent probes are sent to the same base station, typicallyescalating in power level, until either a response is received from thebase station, or the wireless device declares an access failure.

U.S. Pat. No. 5,345,596 discloses a communication access system. Acommunication unit 10 (preferably, a radio telephone headset) isoperable to communicate with one or more base stations. Thecommunication unit 10 transmits channel requests at increasing signalstrengths requesting a communication channel. The first channel requestsignal has a power level that is a predetermined fraction of the maximumoutput of the communication unit 10, and subsequent channel requests aretransmitted at an incrementally higher power level.

Document WO-A-0126411 describes a hand-off system for a cellulartelephone system comprising a plurality of mobile phones and basestations. Communication between a mobile phone and more than one basestation is facilitated by timeslots selected in order to accommodateimitations of the mobile telephone equipment. Handover connection toanother base station and disconnection from a current base station mayalso facilitated by determining a level of communications quality withrespect to the base stations.

SUMMARY

A method of system access to a wireless network, the network having aplurality of base stations, the method comprising the steps of: (a)selecting a reverse link cost metric from a list of reverse link costmetrics; (b) determining a reverse link cost according to the selectedreverse link cost metric; (c) selecting a candidate base station formthe plurality of base stations; (d) sending a probe signal at thereverse link cost to the candidate base station; (e) waiting for aresponse from the candidate base station within a timeout period; and(f) repeating steps (c) to (e) until either the plurality of basestations has been sent a probe at least once at substantially the samereverse link cost and corresponding timeout periods have all expired, ora response is received from at least one candidate base station whereinthe responding candidate base station is used to provide system accessto the wireless network.

According to one embodiment, a method of system access from acommunication device to a wireless network having a plurality of basestations includes the steps of determining a forward link quality foreach of the plurality of base stations, ranking the plurality of basestations according to the forward link qualities for each of the basestations to obtain base station ranks, selecting a reverse link costmetric, determining a reverse link cost according to the selectedreverse link cost metric, and incrementing through the base stationranks and for each base station rank selecting a base station andtransmitting a probe signal based on due reverse link cost from thecommunication device to the selected base station until a response isreceived from a selected base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary wireless device for use in amethod of system access to a wireless network;

FIG. 2 illustrates forward channels and signals of two base stations andthe wireless device of FIG. 1;

FIG. 3 illustrates reverse channels and signals of the wireless deviceof FIG. 1 and the two base stations of FIG. 2;

FIG. 4 is a signal flow diagram illustrating both forward and reversechannel signals of FIGS. 2 and 3;

FIG. 5 illustrates forward channels and signals of four base stationsand the wireless device of FIG. 1;

FIG. 6 illustrates reverse channels and signals of the wireless deviceof FIG. 1 is and the four base stations of FIG. 5;

FIG. 7 is a signal flow diagram illustrating both forward and reversechannel signals of FIGS. 5 and 6 during a first turn at a first reversequality;

FIG. 8 is a signal flow diagram illustrating both forward and reversechannel signals of FIGS. 5 and 6 during a second turn at a secondreverse quality;

FIG. 9 is a flow chart illustrating one example of a method of systemaccess to a wireless network; and

FIG. 10 is a flow chart illustrating another example of a method ofsystem access to a wireless network.

DETAILED DESCRIPTION

Throughout the drawings, the same or similar reference numerals areapplied to the same or similar parts, elements or steps, and thus thedescription of the same or similar parts, elements or steps will beomitted or simplified when possible.

FIG. 1 is a block diagram of a wireless device 10. The wireless device10 is preferably a two-way communication device having at least voice ordata communication capabilities. The device preferably has thecapability to communicate with other computer systems on the Internet.Depending on the functionality provided by the device, the device may bereferred to as a data messaging device, a two-way pager, a cellulartelephone with data messaging capabilities, a wireless Internetappliance or a data communication device (with or without telephonycapabilities).

Where the device 10 is enabled for two-way communications, the devicewill incorporate a communication subsystem 11, including a receiver 12,a transmitter 14, and associated components such as one or more,preferably embedded or internal, antenna elements 16 and 18, localoscillators (LOs) 13, and a processing module such as a digital signalprocessor (DSP) 21. As will be apparent to those skilled in the field ofcommunications, the particular design of the communication subsystem 11will be dependent upon the communication network in which the device isintended to operate. For example, a device 10 destined for a NorthAmerican market may include a communication subsystem 11 designed tooperate within the Mobitex™ mobile communication system, DataTAC™ mobilecommunication system or Code Division Multiple Access (CDMA)communication system, whereas a device 10 intended for use in Europe mayincorporate a General Packet Radio Service (GPRS) communicationsubsystem 11 or a Universal Mobile Telecommunication System (UMTS)communication subsystem 11.

Network access requirements will also vary depending upon the type ofnetwork 20. For example, in the Mobitex and DataTAC networks, mobiledevices such as 10 are registered on the network using a uniqueidentification number associated with each device. In GPRS networks,however, network access is associated with a subscriber or user of adevice 10. A GPRS device requires a subscriber identity module, commonlyreferred to as a SIM card, in order to operate on a GPRS network.Without a SIM card, a GPRS device will not be fully functional. Local ornon-network communication functions (if any) may be operable, but thedevice 10 will be unable to carry out any functions involvingcommunications over network 20 other than ‘911’ emergency calling orother legally required communication functions. When required networkregistration or activation procedures have been completed, a device 10may send and receive communication signals over the network 20. Signalsreceived by the antenna 16 through a communication network 20 are inputto the receiver 12, which may perform such common receiver functions assignal amplification, frequency down conversion, filtering, channelselection and the like, and in the example system shown in FIG. 1,analog to digital conversion. Analog to digital conversion of a receivedsignal allows more complex communication functions such as demodulationand decoding to be performed in the DSP 21. In a similar manner, signalsto be transmitted by the device 10 are processed, including modulationand encoding for example, by the DSP 21 and input to the transmitter 14for digital to analog conversion, frequency up conversion, filtering,amplification and transmission over the communication network 20 via theantenna 18.

The DSP 21 not only processes communication signals, but also providesfor receiver and transmitter control. For example, the gains applied tocommunication signals in the receiver 12 and transmitter 14 may beadaptively controlled through automatic gain control algorithmsimplemented in the DSP 21.

The device 10 preferably includes a microprocessor 39 which controls theoverall operation of the device. Communication functions, including atleast data and voice communications, are performed through thecommunication subsystem 11. The microprocessor 39 also interacts withother device subsystems such as the display 22, flash memory 24, randomaccess memory (RAM) 26, auxiliary input/output (I/O) subsystems 28, USBport 30, keyboard 32, speaker 34, microphone 37, a short-rangecommunications subsystem 41, charging subsystem 44, battery 49 and anyother device subsystems generally designated as 42. When the battery 49eventually becomes depleted, power source 50 is used to charge battery49, and optionally power device 10.

Some of the subsystems shown in FIG. 1 perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as keyboard 32 and display 22for example, may be used for both communication-related functions, suchas entering a text message for transmission over a communicationnetwork, and device-resident functions such as a calculator or tasklist.

Operating system software used by the microprocessor 39 is preferablystored in a persistent store such as flash memory 24, which may insteadbe a read only memory (ROM) or similar storage element. Those skilled inthe art will appreciate that the operating system, specific deviceapplications, or parts thereof, may be temporarily loaded into avolatile store such as RAM 26. It is contemplated that receivedcommunication signals may also be stored to RAM 26.

The microprocessor 39, in addition to its operating system functions,preferably enables execution of software applications on the device. Apredetermined set of applications which control basic device operations,including at least data and voice communication applications forexample, will normally be installed on the device 10 during manufacture.

A preferred application that may be loaded onto the device 10 may be apersonal information manager (PIM) application having the ability toorganize and manage data items relating to the device user such as, butnot limited to, e-mail, calendar events, voice mails, appointments, andtask items. Naturally, one or more memory stores would be available onthe device to facilitate storage of PIM data items on the device 10.Such PIM application would preferably have the ability to send andreceive data items, via the wireless network. In one embodiment, the PIMdata items are seamlessly integrated, synchronized and updated, via thewireless network, with the device user's corresponding data items storedor associated with a host computer system thereby creating a mirroredhost computer on the mobile device with respect to the data items atleast. This would be especially advantageous in the case where the hostcomputer system is the mobile device user's office computer system.

Further applications may also be loaded onto the device 10 through thenetwork 20, an auxiliary I/O subsystem 28, serial port 30, short-rangecommunications subsystem 41 or any other suitable subsystem 42, andinstalled by a user in the RAM 26 or preferably in a non-volatile store24 for execution by the microprocessor 39. Such flexibility inapplication installation increases the functionality of the device 10and may provide enhanced on-device functions, communication-relatedfunctions, or both. For example, secure communication applications mayenable electronic commerce functions and other such financialtransactions to be performed using the device 10.

In a data communication mode, a received signal such as a text messageor web page download will be processed by the communication subsystem 11and input to the microprocessor 39, which will preferably furtherprocess the received signal for output to the display 22, oralternatively to an auxiliary I/O device 28. A user of device 10 mayalso compose data items, such as email messages, for example, using thekeyboard 32, which is preferably a complete alphanumeric keyboard ortelephone-type keypad, in conjunction with the display 22 and possiblyan auxiliary I/O device 28. Such composed items may then be transmittedover a communication network through the communication subsystem 11.

For voice communications, overall operation of the device 10 issubstantially similar, except that received signals would preferably beoutput to a speaker 34, and a microphone 37 would generate signals fortransmission. Alternative voice or audio I/O subsystems, such as a voicemessage recording, subsystem, may also be implemented on the device 10.Although voice or audio signal output is preferably accomplishedprimarily through the speaker 34, the display 22 may also be used toprovide an indication of the identity of a calling party, the durationof a voice call, or other voice call related information for example.

A short-range communications subsystem 41 is a further optionalcomponent that may provide for communication between the device 10 anddifferent systems or devices within close proximity to the device 10,which need not necessarily be similar devices. For example, thesubsystem 41 may include an infrared device and associated circuits andcomponents or a Bluetooth™ RF communication module to provide forcommunication with similarly-enabled systems and devices.

The USB port 30 in FIG. 1 is normally implemented in a personal digitalassistant (PDA)-type communication device for which synchronization witha user's desktop computer may be desirable. Such a port 30 enables auser to set preferences through an external device or softwareapplication and to extend the capabilities of the device by providingfor information or software downloads to the device 10 other thanthrough a wireless communication network. The alternate download pathmay, for example, be used to load an encryption key onto the devicethrough a direct and thus reliable and trusted connection to therebyenable secure device communication. Preferably, the data and powerconnector 47 is used to receive power and data from power/data source50, directing the data to/from USB port 30, and the power to chargingsubsystem 44, so that charging subsystem 44 can recharge battery 49.Software on device 10 preferably reports charging status information tothe user.

Many alternatives to device 10 may be implemented in the system andmethod disclosed herein. Preferably, an alternative to device 10 has atleast a communication subsystem 11 in order to access network 20.Optionally, an alternative to device 10 may also have a battery 49 whosepower may be conserved when implemented in the system and methoddisclosed herein.

FIGS. 2 and 3 illustrate forward and reverse channels of a wirelessdevice 10 accessing a wireless network via two base stations. FIG. 2illustrates the forward channels whereas FIG. 3 illustrates the reversechannels.

Referring now to FIG. 2, a wireless device 10 is in communication withtwo base stations 20A, 20B, each having forward channels within range30A, 30B of wireless device 10, respectively. Wireless device 10receives signals 35A, 35B from base stations 20A, 20B, respectively.Signals 35A, 35B are assumed to be of sufficiently high quality Q_(A),Q_(B), respectively, to be received at wireless device 10. Base stations20A, 20B are candidate base stations for the purpose of providingwireless device 10 system access to a wireless network.

Operationally, wireless device 10 compiles a list of candidate basestations 20A, 20B, by receiving signals 35A, 35B on the forwardchannels. For instance, the candidate base stations can be those in a“Neighbor List” obtained from a base station broadcast with a strongforward link quality.

Alternatively, the candidate base stations may include those basestations of a plurality of base stations whose forward link quality, forinstance signal strength received at the wireless device 10, exceeds acertain threshold. The remaining bases stations are excluded basestations. These candidate base stations are then substituted for theplurality of base stations thereby reducing the cardinality of theplurality of base stations by the cardinality of the plurality ofexcluded base stations.

In FIG. 2, base stations 20A, 20B are disposed at a geometric distancerelative to wireless device 10, which does not necessarily reflectphysical distance between base stations 20A, 20B and wireless device 10.For instance, if signals 35A, 35B are sent over different frequencybands, use different coding or modulation, or are transmitted atdifferent power levels, then base stations 20A, 20B may be illustratedat different geometric distances from wireless device 10 in FIG. 2.Geometric distance in FIG. 2 is inversely proportional to forward linkquality.

The metric used by wireless device 10 to determine the forward linkquality of signals 35A, 35B can be any forward channel characteristicthat is significant to the type of signal received. For instance, signalstrength can be used as one example of a forward link quality metric.Other metrics may be signal to noise ratio, symbol quality, base stationload, or any combination of forward channel characteristics. The choiceof forward link quality metric will impose a bias towards accessing abase station that has a high ranking according to the metric, as will beillustrated in greater detail below.

As shown in FIG. 2, the forward link quality Q_(A) of signal 35A isgreater than the forward link quality Q_(B) of signal 35B (Q_(B)<Q_(A)).Therefore, wireless device 10 ranks base station 20A first over basestation 20B, which is ranked second. Consequently, wireless device 10will preferably probe base station 20A before base station 20B.

Even though base station 20A is ranked first based on forward linkquality, it may be base station 20B that responds 55B first to a probe(shown in FIG. 3) from the wireless device 10 and is used for accessingthe wireless network. This is explained further in regard to FIG. 3,which illustrates the reverse channels.

Referring now to FIG. 3, wireless device 10 has knowledge of the twobase stations 20A, 20B as a result of monitoring forward channelsignals, as was described in reference to FIG. 2. Furthermore, wirelessdevice 10 prefers probing base station 20A before base station 20B sincebase station 20A ranked first using a given forward link quality metric,i.e. Q_(A)>Q_(B). The characteristics of reverse channels available towireless device 10, however, may differ with the characteristics offorward channels, for instance due to different frequency bands,different coding, or modulation.

In FIG. 3, as in FIG. 2, base stations 20A, 20B are disposed at ageometric distance in the drawing relative to wireless device 10 thatdoes not necessarily reflect physical distance between base stations20A, 20B and wireless device 10. Geometric distance in FIG. 3 isinversely proportional to reverse link cost, whereas geometric distancewas inversely proportional to forward signal quality in FIG. 2.

A preferred metric for reverse link cost is power consumption at themobile device 10. Alternate metrics for reverse link cost may be used.

As illustrated in FIG. 3, only base station 20B is within the range 40of probe signals 45A, 45B sent at reverse link cost Cmin, the minimumreverse link cost used in an access attempt by wireless device 10. Basestation 20A is not within the range 40 of probe signals 45A, 45B. Hence,even if base station 20A is probed 45A first in FIG. 3, and base station20B is probed 45B subsequently, base station 20B responds first 55B inFIG. 2 to probe 45B.

Thus, the wireless device 10 conserves energy while accessing thewireless network via base station 20B at the Cmin reverse link cost ofprobe 45B, as compared to accessing the wireless network via basestation 20A at some reverse link cost greater than Cmin.

Having described the forward channels with reference to FIG. 2, and thereverse channels with reference to FIG. 3, a combined signal flowdiagram is described next.

FIG. 4 is a signal flow diagram illustrating both forward and reversechannel signals. The locations of the base stations 20A and 20B as shownin FIG. 4 are inversely proportional to reverse link cost, as in FIG. 3.As those skilled in the art will appreciate, signal lines passingthrough a block or component represent signals that either bypass or arenot processed by that component. Therefore, signal 35A is sent to thedevice 10 by the base station 20A, but as will be apparent from FIGS. 2and 3, the signal 35A is not received or processed by the base station30B.

Wireless device 10 receives signals 35A, 35B over forward channels.Wireless device 10 compares 36A signals 35A, 35B from candidate basestations 20A, 20B in order to rank and select the highest ranked basestation to probe. In the comparison 36A, the forward link quality ofsignals 35A, 35B received by wireless device 10 is determined using agiven metric to determine which of candidate base stations 20A, 20B isranked first and consequently probed first. Thus, the choice of forwardlink quality metric provides a bias towards a particular class of basestation. For instance, if signal strength is the forward link qualitymetric, then base stations with a strong signal will be probed first.Alternatively, if the forward link quality metric is base station load,then base stations with low load will be probed first.

As was illustrated in FIG. 2 and described above, forward link qualityQ_(A)>Q_(B) so base station 20A is ranked first 38A. Consequently,wireless device 10 sends access probe 45A to base station 20A first at aminimum reverse link cost, Cmin.

As illustrated, probe 45A does not reach base station 20A. This may bebecause, in reference to FIG. 3, base station 20A is beyond the range 40of probe 45A at reverse link cost Cmin. Wireless device 10 discoversthis by waiting for a sufficiently long period of time that would haveallowed base station 20A to respond to probe 45A, thereby resulting in afirst timeout condition 46A. Instead of increasing reverse channel rangeby increasing reverse link cost and sending another probe to basestation 20A, however, wireless device 10 then selects the next candidatebase station 20B without increasing reverse link cost. Wireless device10 sends access probe 45B at substantially the same minimum reverse linkcost, Cmin, to base station 20B. Wireless device 10 waits, as indicatedat 48B, for a second timeout condition to occur.

While wireless device 10 is waiting 48B for the second timeout conditionto occur, base station 20B receives access probe 45B and prepares andsends 47B response 55B to wireless device 10. Before the second timeoutcondition occurs, wireless device 10 receives 66B response 55B. Basestation 20B then provides access 67B so that voice and/or datacommunication 75B results between wireless device 10 and base station20B, at reverse link cost Cmin of probe 45B. Thus, wireless device 10,although biased towards probing base station 20A first because of a highforward link quality, will trade-off forward link quality in favor ofminimizing reverse link cost by accessing base station 20B.

Had base station 20B not responded before the second timeout conditionoccurred, wireless device 10 would have had sent at least one probe toall candidate base stations at the Cmin reverse link cost and the probesmay have all timed out, in which case the wireless device 10 would haveincreased reverse link cost, and would have started a second round ofprobes at the increased reverse link cost, beginning with the highestranked base station, 20A.

Accordingly, the wireless device 10 will only increase reverse link costafter having at least once probed all candidate base stations at thecurrent reverse link cost, and after timeout conditions occurred on allprobed candidate base stations at least once. This situation will bedescribed in further detail with reference to FIGS. 5–8, wherein aplurality of base stations is considered.

FIGS. 5 and 6 illustrate forward and reverse channels respectively of awireless device 10 accessing a wireless network via four base stations.FIG. 5 illustrates the forward channels whereas FIG. 6 illustrates thereverse channels.

Referring now to FIG. 5, a wireless device 10 sees four base stations20C, 20D, 20E and 20F each having forward channels within range 30C,30D, 30E and 30F of wireless device 10. Wireless device 10 receivessignals 35C, 35D, 35E and 35F from base stations 20C, 20D, 20E and 20F,respectively. Signals 35C, 35D, 35E and 35F are assumed to be ofsufficiently high forward link quality Q_(C), Q_(D), Q_(E) and Q_(F),respectively, to be received at wireless device 10. As was the case withFIG. 2, geometric distance in FIG. 5 is inversely proportional toforward link quality.

As illustrated, the forward link quality Q_(C) of signal 35C is greaterthan the quality Q_(D) of signal 35D (Q_(D)<Q_(C)). Furthermore, asillustrated, Q_(F)<Q_(E)<Q_(D). Therefore, wireless device 10 ranks thebase stations accordingly: 20C is ranked first, followed by 20D, 20E and20F. Consequently, wireless device 10 will preferably probe base station20C before base station 20D, base station 20D before 20E, and basestation 20E before 20F. This creates a bias towards accessing basestations with high forward signal quality.

Base station 20D responds 55′D first to a probe and is used foraccessing the wireless network. This is explained further in regard toFIGS. 6–8, which illustrate the reverse channels and the process bywhich base station 20D responds 55′D first to the probe.

Referring now to FIG. 6, wireless device 10 has knowledge of four basestations 20C, 20D, 20E and 20F as a result of monitoring forward channelsignals, as was described in reference to FIG. 5. Furthermore, wirelessdevice 10 prefers probing base station 20C first because base station20C ranked first using a given forward signal quality metric, i.e.Q_(C)>Q_(D)>Q_(E)>Q_(F). The characteristics of reverse channelsavailable to wireless device 10, however, may differ with thecharacteristics of forward channels. As was the case in FIG. 3,geometric distance in FIG. 6 is inversely proportional to reverse linkcost.

Probe signals 45C, 45D, 45E, and 45F may be sent over differentfrequency bands, use different coding or modulation, or transmitted atdifferent power levels. Signals 45C, 45D, 45E and 45F, however, are allsent at substantially the same reverse link cost, Cmin as illustrated bytheir common reverse channel range 40.

As illustrated, no base station is within the range 40 of probe signals45C, 45D, 45E and 45F sent at reverse link cost Cmin. Wireless device10, having sent at least one probe to all candidate base stations at theCmin reverse link cost, increases reverse link cost to C1>Cmin, andstarts a second round of probes beginning with the highest ranked basestation 20C. As illustrated, base station 20D is within the range 40′ atreverse link cost C1. Therefore base station 20D receives probe signal45′D, and base station 20D responds first 55′D as shown in FIG. 5.

FIGS. 7 and 8 are signal flow diagrams illustrating both forward andreverse channel signals. Time flows clockwise in both FIGS. 7 and 8.FIG. 7 illustrates in greater detail a first round of probes leading toan increase in reverse link cost whereas FIG. 8 illustrates in greaterdetail a second round of probes at an increased reverse link costproviding access to the wireless network.

Referring now to FIG. 7, as was illustrated in FIG. 5 and describedabove, Q_(C)>Q_(D)>Q_(E)>Q_(F), so base station 20C is ranked first.Consequently, probe 45C is sent to base station 20C first at reverselink cost Cmin.

As illustrated, probe 45C does not reach base station 20C. Wirelessdevice 10 waits for a sufficiently long period of time that would haveallowed base station 20C to respond to probe 45C, and a first timeoutcondition 46C occurs. Wireless device 10 selects the next candidate basestation 20D, to which it sends access probe 45D at substantially thesame minimum reverse link cost, Cmin. Wireless device 10 waits for asecond timeout condition 46D, which occurs. Wireless device 10 thenselects the next candidate base station 20E, to which it sends accessprobe 45E at substantially the same minimum reverse link cost, Cmin.Wireless device 10 waits for a third timeout condition 46E, whichoccurs. Wireless device 10 then selects the next candidate base station20F, to which it sends access probe 45F at substantially the sameminimum reverse link cost, Cmin. Wireless device 10 then waits for afourth timeout condition 46F, which occurs.

Having sent at least one probe 45C, 45D, 45E, 45F to all candidate basestations at the Cmin reverse link cost, wireless device 10 increasesreverse link cost to C1>Cmin, and starts a second round of probesbeginning again with the highest ranked base station 20C.

Referring now to FIG. 8, wireless device 10 sends access probe 45′C atreverse link cost C1>Cmin to base station 20C. Wireless device 10 waitsfor a fifth timeout condition 48′C, which occurs. Wireless device 10selects the next candidate base station 20D, to which it sends accessprobe 45′D at substantially the same reverse link cost, C1. Wirelessdevice 10 waits for a sixth timeout condition 48′D to occur. Whilewireless device 10 is waiting for the sixth timeout condition 48′D tooccur, base station 20D receives 47′D probe 45′D and sends response 55′Dto wireless device 10. Before the sixth timeout condition 48′D occurs,wireless device 10 receives 66′D response 55′D. Base Station 20Dprovides access 67′D, so voice and/or data communication 75′D resultsbetween wireless device 10 and base station 20D, at reverse link cost C1of probe 45′D. Thus wireless device 10 is still biased towardsmaximizing forward link quality even after having to increase reverselink cost.

Having described forward and reverse channels and signal flow diagramsby way of two examples in reference to FIGS. 2–4 and FIGS. 5–8,respectively, a flow chart illustrating the common steps involved in oneembodiment of the method is described next. FIG. 9 is a flow chartshowing an exemplary method of accessing a wireless network.

The method preferably probes all candidate base stations at a particularreverse link cost at least once before escalating the reverse link costthereby ensuring that reverse link cost is minimized. Furthermore, themethod preferably ranks candidate base stations according to forwardsignal quality thereby providing a bias towards maximizing forwardsignal quality that is not at the expense of the aforementionedminimization.

At step 100, wireless device 10 scans forward channels for a pluralityof base stations, or alternatively obtains a “Neighbors List” from atleast one forward channel. The plurality of base stations may beoptionally partitioned into a plurality of candidate base stations and aplurality of excluded base stations to reduce the number of basestations to be processed. The plurality of base stations may also bepreferably ranked according to forward link quality based on a metricselected from a list of predetermined forward signal quality metrics.The list of predetermined forward link quality metrics, in alternateembodiments, may include for example a power consumption metric, asignal strength metric, a coding complexity metric, a modulation typemetric, a network subscriber access cost metric, a bandwidth metric, athroughput metric, a latency metric, a load metric, or a combination ofpredetermined forward link quality metrics. Other metrics may also beused. Illustratively, if a signal strength metric is used, a basestation with a high signal strength will have a higher forward linkquality that a base station with a low signal strength.

The value of a metric may be determined at the wireless device 10 orprovided by the base station, depending on the metric. For example, ifthe metric is a signal strength metric, the value may be determined atthe wireless device 10. Alternatively, if the metric is a load metric ofa base station, the value may be provided by the base station inresponse to the probe signal from the wireless device 10.

At step 110, wireless device 10 determines a minimum reverse link cost,Cmin, which is used as the current reverse link cost C. Preferably, Cminis determined as a function of the highest ranked forward link quality,as a higher forward link quality yields a lower Cmin. As previouslydescribed, the reverse link cost can be, for example, based on themetric of power consumption at the wireless device 10. Preferably, thereverse link cost is determined based on a reverse link cost metricselected from a list of predetermined reverse link cost metrics. Thelist of predetermined reverse link cost metrics, in alternateembodiments, may include, for example, a power consumption metric, atransmitted power metric, an interference level metric, a coding typemetric, a modulation type metric, a network subscriber access costmetric, a bandwidth metric, a throughput metric, a latency metric, aload metric, or a combination of predetermined reverse link costmetrics. Other metrics may also be used.

If base stations are ranked or otherwise biased in favor of selectinghigh forward link quality base stations first, then at step 120,candidate base stations that are higher ranked are probed first. Thisbias maximizes forward signal quality without increasing reverse linkcost. In alternate embodiments, the candidate base stations can beranked in a pseudo-random manner without regard to forward signalquality, or optionally not necessarily ranked so long as a bias ismaintained in selecting a candidate base station to favor a base stationwhich has a high forward link quality relative to the plurality of basestations according to the selected forward link quality metric

At step 120, the candidate base stations obtained at step 100 aresuccessively considered in turn. If the base stations are ranked orotherwise biased by order determined by a rank index, such as such as bydecreasing forward link quality, the candidate base stations may besuccessively considered according to the rank index. Selected basestation are probed at step 130 and monitored at step 140, until eitherall base stations are processed at step 160, or until access is grantedat step 150.

Probing according to high forward link quality first favors access tobase stations which rank highest according to the selected forward linkquality metric, such as for example base stations with high forwardsignal strength. This is done without increasing reverse link cost. Theranking preferably occurs on the basis of a forward link quality metricselected from a list of predetermined forward link quality metrics.

At step 130, the current candidate base station is sent a probe over thereverse channel at the current reverse link cost C, which was firstdetermined at step 110, and which may have been increased in subsequentturns at step 170. This ensures that reverse link cost is minimized asall base stations are processed at the current reverse link cost beforeincreasing reverse link cost.

At step 140, the current candidate base station is monitored over theforward channel for a response to the probe sent at step 130. If aresponse is received within a timeout period, then access to the networkensues over the current candidate base station at step 150. If aresponse is not received within the timeout period, however, then step160 verifies if all candidate base stations have been processed in thisturn at the current reverse link cost. In alternate embodiments, morethan one probe signal can be sent to more than one candidate basestation so that the timeout periods for two or more base stations may becontemporaneous and multiple base stations are monitored simultaneouslyfor response thereby improving network system access time.

At step 160, if all candidate base stations have been processed in thisturn at the current reverse link cost, then step 170 follows, and thereverse link cost C is increased. If not all candidate base stationshave been processed at the current reverse link cost, however, then thenext base station in the rank order is selected as the current basestation at step 120.

At step 170, the current reverse link cost C is increased according to agiven metric for reverse link cost, for instance by augmenting transmitpower, channel coding, or both.

At step 180, if the current reverse link cost C has past a certainpredefined limit, for instance the capacity of wireless device 10, thenaccess failure is declared at step 190. If the current reverse link costC is still within limits, then another turn ensues at step 120, whereatanother current candidate base station is selected, however, beginningwith the highest ranked, and the processing in steps 130 through 180 isrepeated at the increased reverse link cost.

At step 190, all candidate base stations have been probed at least onceat the maximum reverse link cost, so an access failure is declared.Preferably the wireless device 10 then scans for alternate candidatebase stations.

In an alternate embodiment, more than one access probe may be sent to acandidate base station at substantially the same reverse link costbefore the next candidate base station is probed.

FIG. 10 provides a flow chart illustrating another example of a methodof system access to a wireless network. In step 200, the wirelesscommunication device 10 determines a forward link quality for each of aplurality of base stations.

In step 210, the base stations are ranked according to the forward linkquality of each base station to obtain base station ranks. Thus, thebase station with the higher signal strength will be ranked higher thanthe base station with the lower signal strength.

In step 220, the wireless communication device 10 selects a reverse linkcost metric and determines a reverse link cost according to the selectedreverse link cost metric.

In step 230, a base station corresponding to the first base station rankis selected, and in step 240 the wireless communication device 10transmits a probe signal to the selected base station based on thereverse link cost.

In step 250, the wireless communication device 10 determines if aresponse is received from the selected base station in response to thereverse link cost probe. The wireless communication device 10 maydetermine whether a response is received by one or more measurementcriteria. For example, the received response may be required to exceed asignal to noise ratio, or may be required to be received within atimeout period. If the received response does not meet the measurementcriteria, then the wireless communication device 10 will deem that nosignal is received.

If a response is received, then access to the network ensues, as shownin step 260. If no response is received, then the wireless communicationdevice 10 determines if it has reached the end of the base station rankin step 270. If the end of the base station rank has not been reached,then the next base station in the base station rank is selected in step280, and steps 240–280 are repeated accordingly. If the end of the basestation rank has been reached, however, then the wireless communicationdevice 10 determines if the reverse link cost exceeds a threshold limitin step 290. If the reverse link cost does not exceed the thresholdlimit, then the reverse link cost is increased in step 300, and steps230–290 are repeated accordingly. If the reverse link cost does exceedthe threshold limit, then the wireless communication device 10determines that them is a failure to establish communication with thewireless network.

1. A method comprising the steps, performed by a wireless device for accessing a wireless network through network base stations, of (a) selecting a reverse link cost metric from a list of reverse link cost metrics; (b) determining a reverse link cost according to the selected reverse link cost metric; (c) selecting a candidate base station from a plurality of the base stations (d) sending a probe signal at the reverse link cost to the candidate base station; (e) waiting for a response from the candidate base station within a timeout period; and (f) repeating steps (c) to (e) until either the plurality of base stations has been sent a probe at lest once at substantially the same reverse link cost and corresponding timeout periods have all expired, or a response is received from at least one candidate base station wherein the responding candidate base station is used to provide system access to the wireless network, further comprising the steps of: (g) selecting a forward link quality metric from a list of forward link quality metrics: and (h) biasing the selection of the candidate base station at step (c) toward base stations having a high forward link relative to the plurality of base stations according to the selected forward link quality metric; (i) partitioning the plurality of base stations into a plurality of candidate base stations and a plurality of excluded base stations, wherein each of the plurality of candidate base stations has a candidate forward link quality which exceeds a threshold; and (j) substituting the plurality of base stations with the candidate base stations thereby reducing the cardinality of the plurality of base stations by the cardinality of the plurality of the excluded base stations; wherein the step (h) of biasing the selection of the candidate base station comprises the steps of: (k) ranking the plurality of base stations according to forward link quality; and (l) in step (b) selecting highest ranked base station which has not yet been probed at the reverse link cost.
 2. The method of claim 1, fiber comprising the steps of: (m) partitioning the plurality of base stations into a plurality of candidate base stations and a plurality of excluded base stations; and (n) substituting the plurality of base stations with the candidate base stations thereby reducing the cardinality of the plurality of base stations by the cardinality of the plurality of excluded base stations.
 3. The method of claim 1, further comprising the steps of: (o) increasing reverse link cost after Step (f), and then (p) repeating the steps (c)–(h) until either system access to the wireless network has been provided, or the reverse link cost exceeds a threshold.
 4. The method of claim 1, wherein the list of reverse link cost metrics comprises a power consumption metric.
 5. The method of claim 1, wherein the list of reverse link cost metrics comprises a transmitted power metric.
 6. The method of claim 1, wherein the list of reverse link cost metrics comprises interference level metric.
 7. The method of claim 1, wherein the list of reverse link cost metrics comprises a coding type metric.
 8. The method of claim 1, wherein the list of reverse link cost metrics comprises a modulation type metric.
 9. The method of claim 1, wherein the list of revere link cost metrics comprises a network subscriber access cost metric.
 10. The method of claim 1, wherein the list of reverse link cost metrics comprises a bandwidth metric.
 11. The method of claim 1, wherein the list of reverse link cost metrics comprises a throughput metric.
 12. The method of claim 1, wherein the list of reverse link cost metrics comprises a latency metric.
 13. The method of claim 1, wherein the list of reverse link cost metrics comprises a load metric.
 14. The method of claim 1, wherein the list of reverse link cost metrics comprises a combination of reverse link cost metrics.
 15. The method of claim 1 wherein the step (b) of determining a reverse link cost depends on a forward link quality for each of the plurality of base stations.
 16. The method of claim 1, wherein the step (c) of selecting a candidate base station is pseudo-random.
 17. The method of claim 1, wherein any of the steps (c) through (e) are executed in parallel for at least two candidate base stations.
 18. The method of claim 1, wherein the list of forward link quality metrics comprises a power consumption metric.
 19. The method of claim 1, wherein the list of forward link quality metrics comprises a signal strength metric.
 20. The method of claim 1, wherein the list of forward link quality metrics comprises an interference level.
 21. The method of claim 1, wherein the list of forward link quality metrics comprises a coding complexity metric.
 22. The method of claim 1, wherein the list of forward link quality metrics comprise a modulation type metric.
 23. The method of claim 1, wherein the list of forward-link quality metrics comprises a network subscriber access cost metric.
 24. The method of claim 1, wherein the list of forward link quality metrics comprises a bandwidth metric.
 25. The method of claim 1, wherein the list of forward link quality metrics comprises a throughput metric.
 26. The method of claim 1, wherein the list of forward link quality metrics comprises a latency metric.
 27. The method of claim 1, wherein the list of forward link quality metrics comprises a combination of forward link quality metrics.
 28. A method comprising the steps, performed by a mobile wireless device configured to access a wireless network through base stations, of: sending a first probe signal at a first reverse link cost to a base station and waiting for a response, for each base station of a set of base stations; if no response to the first probe signal is received from each base station within a preset first time period, then sending to each of at last one of the base stations a second probe signal at a second reverse link cost greater than the first reverse link cost and waiting for a response; and if a response to the second probe signal is received from one of the base stations within a preset second time period, then accessing the network through that responding base station, further comprising before the sending step: determining which base stations, from a plurality of base stations, to include in the set by receiving forward channel signals from the plurality of base stations and including in the set only those stations of the plurality from which the forward channel signals have a forward link quality above a threshold, wherein the forward link quality is signal strength.
 29. The method of claim 28 wherein the first and second reverse link costs correspond respectively to a first signal strength and a second signal strength greater than the first signal strength.
 30. The method of claim 28 further comprising: if response to the first probe signal is received from one of the base station within the first time period, then accessing the network through that responding base station.
 31. The method of claim 28 wherein the sending step includes sending the first probe signal to each base station in sequence.
 32. The method of claim 31 wherein the sequence is in order of decreasing forward link quality of forward channel signals received from the base stations before the sending step.
 33. The method of claim 31 wherein the sending step includes: after sending each first probe signal to the respective base station in the sequence, waiting a preset time period to receive a response from the respective base station before sending the next first probe signal to the next base station in the sequence. 